Electron discharge device



July 12, 1960 J. H. JOHNSTONE ETAL 2,94

ELECTRON DISCHARGE DEVICE 2 Sheets-Sheet, 1

Filed June 13, 1958 INVENTORS ATTORNEY July 12, 1960 J. H. JOHNSTONE ETAL 2,945,147

ELECTRON DISCHARGE DEVICE I Fil ed June 13. 1958 2 Sheets-Sheet 2 RESISTANCE VS TIME RESISTANCE (OHMS) ]NVENTOR. JOHN H. JOHNSTONE BY KEITH w. OLSON ATTORNEY ELECTRON DISCHARGE nnvrcn John H. JohhstonaShrewsbury, and Keith W. Olson,

Neptune, N.J., assignors to Bendix Aviation Corporation, Eatontown, N.J., a corporation of New Jersey Filed June 13, 1958, Ser. No. 741,900

4 Claims. (Cl. 313-217) The present invention relates to electronic discharge devices and more particulary to electron discharge devices adapted to indicate elapsed time of use.

In many applications it is desirable to have an electrical device which can be easily installed in an operating circuit to indicate the total elapsed time of use of the circuit. Such a device should be small in physical size and require only a small amount of current for opera tion. I

Current devices include a tube in which material is evaporated from a hot filament, and the resistance of the evaporated material between two conductors is meas-' ured as a function of time. Another type of device utilizes the principle of electroplating with the electrodeposited material used as an indication of elapsed time.

In devices of the evaporation type, it has been difiicult to achieve a reproducible geometry, secure reproduci ble initial conditions and to have a sufficiently low power requirement. Using electroplating requires a tube filled with a liquid electrolyte which is undesirable in many applications because of breakage problems and temperature limitations.

The present invention provides 'a device which utilizes sputtering of material by the process of bombarding an electrode with ionized gaseous particles and in which the sputtered material is deposited in such a manner that the resistance of the material deposited decreases as a function of time.

It is an object of the invention to provide'an improved elapsed time of use indicator.

Another object of the invention is to provide a novel elapsed time of use indicator having a low power requirement.

Another object of the invention is to provide an improved elapsed time of use indicator that is simple to manufacture and has easily reproducible geometry.

The above and other objects and features of the invention will appear more fully hereinafter from a consrderation of the following description taken in connection with the accompanying drawing wherein one embodiment is illustrated by way of example.

In the drawing:

Figure l is a cutaway view of a device embodying the lnventlon.

Figure 2 is a curve illustrating the resistance-time characteristics of the device.

Figure 3 is a schematic diagram of a typical operating circuit.

Referring now to the drawing, an electron discharge device is indicated generally by the numeral 5 and has an envelope 6 of glass or other suitable material. The envelope 6 includes a button stem section 7.

An anode 8 of nickel or other suitable material is connected by lead 9 to pin 10 which extends through the stem 7. The anode 8 extends through mica spacers 11 and 12. The spacers 11 and 12 are positioned on the anode 8 by eyelets 13 or in any other conventional man- A 2,945,147. Patented .July 12,1960

ice

the spacer 11.

The mica spacer 12 is also supported by insulators 15 through which pins 16 extend. Connected to the pins 16 is a thin wire cathode 17 of a suitable material for example molybdenum, which is concentric with the anode 8 and rests on the mica spacer 12.

Conductive coatings 18 and 19 are provided on the inside surface of the envelope 6 and are positioned diametrically opposite. The coatings 18 and 19 may be thin strips of silver painted on the envelope. Other conductive coatings may be used. Snubber contacts 20 and 21 are provided for making electrical contact with the strips 18 and 19 respectively. The contact 20 is connected to pin 22 and the contact 21 is connected to the pin 23. The envelope 8 may be filled with an inert gas, such as a mixture of argon and neon.

In operation, the device utilizes sputtering of material by the process of bombarding an electrode with ionized gaseous particles in which the sputtered material is deposited on the inner surface of the envelope and the resistance of the deposited material measured between two conductive strips decreases as a function of time. The cathode material, gas and diode geometry, are selected from the known characteristics thereof, to yield a pre; determined sputtering rate of the cathode material for a given tube drop and tube current. The sputtered material is deposited on the walls of the envelope and with the device de-energized the resistance between the two contacts on the wall is measured as a function of time. The cathode size is selected so that the device operates at a normal glow discharge in the current range desired. Thus, the sputtering rate may be controlled by a change of cathode size, change in cathode material, gas composition, gas pressure or tube geometry.

Figure 2 is a typical resistance-time characteristic curve. For a given design the resistance-time characteristic is shown by the solid line. After a device has been aged for a predetermined time, its resistance is measured and its resistance-time characteristic will follow the same slope as the solid line and is indicated by the dashed line.

Figure 3 is a typical circuit for operation of the device. The anode 8 is connected by conductor 10 to one side of a suitable source of potential (not shown). A resistor 24 and ammeter 25 may be inserted in the conductor 10. The cathode 17 is connected by conductor 16 to the other side of the source of potential. To measure the resistance of the sputtered material an ohmmeter (not shown) is connected across the terminals 22 and 23.

Although only one embodiment of the invention has been illustrated and described, various changes in the form and relative arrangement of the parts, which will now appear to those skilled in the art, may be made Without departing from the scope of the invention.

What is claimed:

1. An electron discharge device comprising a gas filled envelope, a rod like anode, a ring like molybdenum cathode concentric with said anode, pin means for making electrical connections to said anode and cathode, a pair of diametrically opposite conducting strips on the interior surface of said envelope, and other pin means for making electrical connections to said conducting strips whereby the resistance of sputtered material from said cathode on said envelope may be measured.

2. An electron discharge device adapted for use as an elapsed time of use indicator, comprising a glass envelope, an ionizable gas filling for said envelope, a rod like anode, a thin wire cathode concentric with said anode, said cathode being of a material having a predetermined sputtering rate when bombarded with ionized gaseous particles, a pair of diametrically opposite conducting strips on the interior surface of said envelope, and means for measuring the resistance of the sputtered material from said cathode collected on the interior surface of said envelope between said strips to give an indication of elapsed timeof use.

said cathode material is molybdenum. 4. A device adapted to be plugged into an operating circuit to indicate the total elapsed time of use of the circuit, comprising an envelope having a filling of ioniza- 10 2,095,930

ble gas, an electrode of a material having a predetermined sputtering rate, means for bombarding said electrode with ionized gaseous particles, and means for measuring the material sputtered from said electrode to give an indica- 5 tion of total elapsed time of use. 3. The combination as set forth in claim 2 in which References fitted in the file of this patent UNITED STATES PATENTS Houtermans e't a1. Oct. 12, 1937 

